182 REPORTS ON THE STATE OF SCIENCE.—1914. 
is closed, and the thermometer therefore screened from the action 
of the gas. In this way the thermometer is withdrawn just before 
the end of compression, so that at this critical period of the cycle 
there is nothing in the shape of a protuberance to cause preignition. 
When the platinum thermometer is exposed in the cylinder and 
connected to the Wheatstone bridge and galvanometer on which the 
indications are received, the circuit is made by a contact-maker on the 
crank-shaft when the crank passes through an assigned crank-angle, and 
is broken by the contact-maker when the crank passes through a second 
assigned crank-angle a little greater than the first, so that the electrical 
ll fe 
MY 
INSULATION® 
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4 
OF AAMFPING 
Sczew Ste tie 4. 
Fig. 3. 
measuring device is in operation during 5°, 10°, or 15° as the case 
may be. 
This contact-maker is a very important part of the electrical equip- 
ment used in connexion with these temperature measurements, as it 
enables a definite make and a definite break to be made in the electrical 
circuit, and, in addition, enables the time between the make and break 
to be adjusted with accuracy. 
The contact-maker (fig. 3). consists of a brass bush B, keyed to a 
lay shaft of the engine, and carrying two fibre washers or cains W, and 
W:, which can be clamped in any relative angular position against the 
flange of the bush by the nut N. A radial step, as w, is made in 
each washer, and the surface gradually rises from the bottom of the 
step to the normal circular surface of the washer. The reflexed ends 
